EO Hoppé is one of the pioneers of street photography. The National Portrait Gallery's current exhibition, which ends on 30 May, includes his shots of ordinary people – bus drivers, postmen, circus performers – in London between the wars, as well as his more famous portraits of society figures.

The NPG, having noted that many of Hoppé's locations remain familiar today – London Zoo, Hyde Park, the Savoy Hotel – invited the public to respond to Hoppé's street scenes with images of their own. The crowdsourced result, as might have been expected, is a mixed bag. The 2,500-plus entries can be seen on this Flickr pool. Some have aimed to recreate the mood, and even the era, of Hoppé's pictures in black and white. Others have used his images as a tangential starting point to capture the vibrancy of today's city in colour and movement.

The five winning images, on display at the gallery until the show closes, just about cover the waterfront in terms of stylistic nods to Hoppé. I love Simon 64's short series of portraits of one daydreaming man on the tube, though they are more Walker Evans than Hoppé. The portrait of Rosa looking out of a window at a farewell scene by Tom Rosenthal manages to be contemporary and timeless, as well as intimate on several levels. Maciej Dakowicz has gone for the graphic approach and captured after-hours Cardiff in all its dissolution. The fact that the prone girl lying in front of the overflowing rubbish bin is entitled Happening – Cardiff makes me think it was staged. I hope so just because it is diametrically at odds with the reverent approach to Hoppé that prevails in, say, skernsnapper's black-and-white shot of young children on a street in Kilburn. It looks like time has stopped in the late 1950s here, making it more Shirley Baker than Hoppé. Ambra Vernuccio's street portrait of a young boy and a toddler in a wrecked car in Umoja is hardly Hoppé at all, but it's a great photograph that also manages to point up the oddly meaningless rules at work here.

What does this all add up to, though? Galleries getting hip to interactivity in a way that, say, newspapers already have? A new way of encouraging people to look at photography more closely? Or another way of endorsing the much-held but mistaken view that, of all the arts, photography is the one that anyone can do? (And please don't start up with the so-tired-as-to-be-embarrassing "photography isn't art" line.) Some people think this is a trend that will continue and expand in the future, allowing audiences to respond creatively to current exhibitions.

I'm not so sure. I'm fine with people responding to great photography, I'm just not sure how instructive the results are, or if, in a world already overcrowded with images, I want to see another batch of mildly interesting ones. That's not what I go to an art gallery for.